Apparatus for viewing

ABSTRACT

The invention applies a viewing system used for reproduction or proofing based on the colorimetric analysis, the characteristics of which are based on the fact that the external conditions affecting the visual color impression of the screen image or other non-reflecting image and of the reflecting image the same. Furthermore, as all the colors in the images have the same chromaticity and luminance, the internal charcteristics of the images do not distort the total color impression, either. In the viewing system the screen or other non-reflecting image (1) is placed behind a uniformly illuminated, usually medium gray, viewing plane (4). The viewing plane is provided with an opening of the same size and shape as the reflecting image, through which viewer sees a part of the screen or other non-reflecting image, and another opening for the reflecting image (6).

The object of the invention is a viewing system which can be used forcomparing reproduced and proof images, or for studying a non-reflectingimage alone. Generally, it is advisable to use a colour definitionmethod based on colorimetry in all applications of the technique inwhich the colours should be described unambiguously and precisely. Thecolorimetric method has been used and is still used in certain (not somany) colour reproduction equipment applications. Generally taken, thissubject has been studied relatively little. As for commercialapplications, the principles have not made a breakthrough into theprinting trade. One reason for this is the lack of accurate and usableinformation on the factors affecting the perception of colours and thereproduction of colours in the reproduction process.

Numerous factors connected with the surroundings of the image and theimage itself affect the colour effect given by the image, so there is noaccurate quantitative method for describing how the colour effectappears. Many reproduction and proofing methods based on colorimetriccolour analysis, some of which have been refined over the years, do notgive satisfactory results, since the visual colour effect and itsrepeatability cannot be controlled. Even if these methods would givesatisfactory results in practical use, the quantification of the coloureffect and controlling its repeatability usually present a majorproblem.

Using the now-invented viewing system it has been possible to solve theabove-mentioned problem in a limited scope with digital definition ofthe colour effect. This is based on the fact that when using the viewingsystem, different types of images will give a similar visual effect,provided the chromaticity defined with the colorimetric method, and theabsolute luminance are the same for each colour in the images to becompared.

The now-invented system consists of a box, a viewing plane on the rearwall of the box, an opening in the viewing plane for the reflecting andnon-reflecting image, equipment for illuminating the viewing plane andthe reflecting image, and in the front wall of the box, a viewingopening. The box is ideally lined with a material reflecting as littlelight as possible. The light should ideally simulate daylight. Theillumination system is such that no light is projected onto thenon-reflecting image. This can be achieved e.g. by placing thenon-reflecting picture behind the viewing plane. Ideally, the viewingplane and the images to be viewed are parallel to each other. Theviewing opening is ideally placed symmetrically with reference to theimages. The size and shape of the image openings depend on the size andshape of the images to be viewed. Moreover, the edges of the openingsare preferably lined with material reflecting as little light aspossible.

The viewing plane is usually medium grey, but it can be lined forexample with the printing paper to be used.

When the non-reflecting image is behind the viewing plane, the edges ofthe opening in the viewing plane, and the duct between the opening andthe image surface, are coated with a material (e.g. black) reflecting aslittle light as possible. The person viewing the image will see thelining of the interior walls, as the image is confined to the viewingplane surface.

The reflecting image can essentially be placed on viewing plane (wherebythe distance between the image and the plane can, for example, be equalto the thickness of the paper with which the plane is lined).

Both the reflecting image and the non-reflecting image can be placedbehind the plane, preferably at the same distance.

Both the viewing plane and the reflecting image can be illuminated withsame lighting fixtures. There can, for example, be two lighting fixturesplaced on opposite sides of the viewing plane, or for example four ormore lighting fixtures placed of various sides of the viewing plane.

There can also be separate lighting fixtures for the viewing plane andthe reflecting image. In this case, the viewing plane is asemi-translucent diffuse surface illuminated from behind. The reflectiveimage can be illuminated from the front so that the light falls only onthe reflecting image.

Some modifications of the invention are described in detail withreference to the attached drawings, whereby FIGS. 1a and 1b are aschematic view of the now-invented viewing system, as seen from the sideand above; FIG. 1c shows the viewing plane as seen from the front; andFIGS. 2a, 2b, 2c as well as 3a, 3b and 3c display two more now-inventedsystems as seen from the same angles.

The viewing system in question was developed for use with thereproduction method based on colorimetric colour analysis. However, thesystem can be used in principle with any colour separation equipment.Using a test run and the method described--e.g. in the article Laihanen,P. Colour Reproduction Theory Based On The Principles Of Colour Science.IARIGAI, 19th International Research Conference. May 31 - Jun. 6, 1987,Eisenstadt (the said article is attached hereto)-it is possible todefine for any standardized reproduction process the interdependence ofthe colours used (e.g. cyan C, magenta M, yellow Y, black K) and thecolorimetric colour values. If the (digitalized) CMYK values of theimage colour separated with the appropriate reproduction process areknown, it is possible to calculate the colorimetric colour value and,furthermore, the image colour parameters of a screen or othernon-reflecting image that give the appropriate colour as defined withthe colorimetric analysis. In this way it is possible to obtain a "softproof" with a reproduction method which does not apply the principles ofthe colorimetric colour analysis. If the screen or other non-reflectingimage can reproduce all the colours of the reflecting image, an accurateproof can be made of any image, when its colorimetric colour values inconditions similar to those in the viewing system displayed in thefigures are known, or they can be calculated using the method describedin the before-mentioned article or some other method. To facilitate thecomputation of the colour values, the chromaticity and the luminance ofthe light reflected from the reference white on the viewing plane (e.g.pressed barium sulphate powder) should be standardized, whereby it is inprinciple possible to make the required colour measurements andcomputations without the viewing system. The non-reflecting image refersto either to a self-illuminating image based on the colour additivemethod, such as the CRT, or a translucent image provided with its ownlight source.

The figures show equipment in which, when viewing the colour screen orother non-reflecting image and the reflecting image, the colours arevisually similar to each other, provided the chromaticity defined withthe colorimetric method (e.g. the CIE x and y values) and the luminanceare the same for all the colours in the image. The visual equivalencehas been experimentally proven. In particular, it should be noted thatlightness is expressed as absolute luminance value (cd/m²) and not asrelative lightness.

As shown in FIGS. 1 and 2, the colour screen or other non-reflectingimage 1 is placed behind the usually medium grey viewing plane 4 orrespectively 10, which is illuminated with the lamps simulating naturaldaylight. Medium grey may be replaced with some other colour. In somecases, the viewing plane may, for example, be lined with the paper usedfor printing. In the viewing plane is the opening 7, usually square orrectangular, and of the size and shape of the reflecting image, throughwhich the person looking into the system sees a part of the screen orother non-reflecting image. The viewing plane is also provided with theopening 8 for the reflecting image 6. Viewing of different-sizedpictures is also possible. Normally, openings of various sizes ordigital image format conversion should be used to give images ofequivalent size. The viewing system is so designed that no light fromthe lamps illuminating the reflecting image and the viewing plane fallson the screen or on another, non-reflecting image. Moreover, to avoiddistracting reflections, the frame and the edges of the area between theviewing plane and non-reflecting image surface are lined with a material5, such as black velvet, reflecting as little light as possible. Toensure visual equivalence, the reflecting image is also placed behindthe viewing plane.

In the system shown in FIG. 1, the distance between the image surfaceand the viewing plane 4 is very small (e.g. the thickness of the sheetof paper on the viewing plane), so that there is no change in the lightfalling on the image surface, except in microscale along the edges. Theother alternative is to place the screen or other non-reflecting imageand the reflecting image at an equal distance from the viewing plane, asshown in FIG. 2.

Placed symmetrically in respect of the images at a suitable distancefrom the viewing plane, the images are viewed through the opening 3. Theviewer will not see the edges of the screen or other non-reflectingimage, nor the black lining of the opening, as the images are confinedto the uniformly illuminated viewing plane surface.

The characteristics of the viewing system are based on the fact that theconditions affecting the visual colour impression given by the screen orother non-reflecting image and the reflecting image are the same. Andsince the chromaticity and luminance of all the image colours are thesame, the internal factors of the image will not cause any differencesin the total colour impression, either.

In the viewing system shown in FIG. 3 the diffuse. translucent viewingplane 11 is backlit with the lighting fixture 2. The reflecting picture6 is illuminated frontally with the spotlight 12. The spotlight 12 onlyilluminates the part of viewing plane 11 covered by the reflecting image6. The viewing plane 11 is provided with the opening 7 for the screen 1.The images are viewed through the opening 3. The inner walls 5 of theconstruction are made of a material reflecting as little light aspossible.

The basic principle with the system as shown in FIG. 3 is to achieve (asin FIGS. 1 and 2) a uniform viewing environment for the image on thescreen and the reflecting image.

The viewing system is well suited for comparing the screen image orother non-reflecting image and a reflecting image. However, in the earlystages of reproduction there is (of course) no reproduced imageavailable. In such a case, the screen image or other non-reflectingimage is viewed on its own. Thus it is possible to the use the screenimage or other self-illuminating image both as a tool for interactiveimage processing and as a high quality "soft proof".

I claim:
 1. A system for viewing a reflecting and/or a non-reflectingimage, to be used for reproduction or proofing based on colorimetricanalysis, comprising:a box with a rear wall and a front wall; a viewingplane on the rear wall of the box; a first opening in the viewing planefor a reflecting image; a second opening in the viewing plane for anon-reflecting image; means for uniformly illuminating the viewing planeand the reflecting image visible through the first opening in theviewing plane without illuminating the surface of the non-reflectingimage visible through the second opening in the viewing plane; a viewingopening in the front wall of the box through which the reflecting imageand the non-reflecting image can be viewed simultaneously.
 2. A viewingsystem as set forth in claim 1, in which the non-reflecting image isessentially placed behind the viewing plane.
 3. A viewing system as setforth in claim 1, in which the reflecting image is essentially placedbehind the viewing plane.
 4. A viewing system as set forth in claim 1,in which the reflecting image and the non-reflecting image are placed atsubstantially the same distance behind the viewing plane.
 5. A viewingsystem as set forth in claim 1, in which the means for illuminatingconsists of light sources which illuminate both the reflecting image andthe viewing plane.
 6. A viewing system as set forth in claim 1, in whichthe means for illuminating comprises separate light sources forilluminating the reflecting image and for illuminating the viewingplane.
 7. A viewing system as set forth in claim 1, in which the viewingplane is a semitranslucent, diffuse plane illuminated from behind.
 8. Aviewing system as set forth in claim 1, in which the viewing plane has amedium grey surface.
 9. A viewing system as set forth in claim 1, inwhich the viewing plane has a surface which is lined with a printingpaper.
 10. A viewing system as set forth in claim 1, in which both thesize and the shape of the first and second openings for the reflectingimage and the non-reflecting image can be adjusted according to the sizeand the shape of the image to be viewed.